An auxiliary lock is an extra reinforcing device used for attachment to a door, in addition to an ordinary latching knob-actuated lock, for safety. When fixing this lock in a door, a long latitudinal groove needs to be cut on the side surface of a door so as to fit the lock in. A turning hole then is cut in the front surface of the door to fit with an intersecting "crossed hole" of the lock. The "crossed hole" is a rotatable member having a cross-shaped opening.
Usually, locks nowadays manufactured have a certain definite distance between its crossed hole and faceplate. So users have to properly select the size of a lock according to the structure of a door (namely, the length of the long latitudinal groove in the door) that the lock is to be fixed on. But, in order to satisfy different needs, manufacturers have to make auxiliary locks of different sizes, retailers are obliged to devote more space for storing them, and besides, buyers may feel at a loss in selecting them.